Surface Plasmon (abbreviated as SP) is a vibration mode that is formed by the collective oscillation of metal surface electric charges and propagates along an interface between a metal and a dielectric; a surface plasmon wave is present on the interface of two materials with opposite signs of dielectric constants (generally being a metal and a medium). Surface Plasmon Resonance (abbreviated as SPR) is a physical optical phenomena that is a surface plasmon oscillation phenomena of an optical wave generated on the interface of two mediums with opposite signs of dielectric constants (such as the interface of a metal and a medium). The energy of an incident optical wave can be coupled into the plasmon wave using the method of prism-coupling Attenuated Total Reflection (abbreviated as ATR): when a linear polarization surface optical wave with the electric component parallel to the incident plane is incident on the interface in a specific angle, the wave vector of the surface plasmon wave matches that of the evanescent wave, which is parallel to the interface, the energy of the incident light is coupled into the surface plasmon wave. At this specific angle, the energy of the reflected light decreases dramatically, forming a downward sharp peak, i.e., a SPR is generated. At this moment, the corresponding specific incident angle is called as surface plasmon resonance angle (abbreviated as SPR angle). Since the generation of the SPR closely relates to the refractive index and thickness of the medium contacting the metal, the SPR can be used as a sensor to detect the refractive index of different solutions and the biochemical reaction happening at the metal interface.
A SPR sensor plays an important role in many aspects of detection due to its high sensibility and real-time detection ability. At present, the angle scan detection method is the most common detection method adopted by the SPR sensor. This method can be used to detect an SPR angle to thereby obtain a series of important parameters, such as the dielectric constant of the detected medium on the surface. Therefore, the determination of the SPR angle is one of the key technologies for the SPR sensor.
Nowadays, according to the typical angle scan detection method, a light source having a fixed wave length is used, said incident angle is changed by using a focus light beam distributed in a certain angle or by using a rotary table, to obtain the intensity of the reflected light under all incident angles, and thereby obtaining an angle position corresponding to the peak value of the reflected light intensity curve (this peak value refers to the minimum value of the intensity of the reflected light, which is called as SPR peak), the SPR angle is then determined according to the position of said peak value. However, due to the limitation to the instruments, the interval of angle scan cannot be shortened unlimitedly, the intensities of the reflected light actually measured are some discrete values, while the resonance peak including the SPR angle is not symmetrical, moreover, during the process of detection, the offset of the resonance angle caused by the variation of dielectric constants of the detected object is usually very small, all these bring a big problem to an accurate determination of said resonance angle, currently the methods of processing the obtained data are mainly as follows: centroid method, multinomial fitting, dynamics baseline, etc., these methods can be used to obtain the relatively precise data concerning resonance angle, however, these data are obtained on the basis of acquiring experiment data and then processing said data experience in a complex way using the abovementioned methods, therefore, the offsets and errors occurring in real time during the process of experiment will affect the final result; the data processing algorithm to be realized is quite intricate, complex hardware or software is required, thus limiting the lowering of system cost; in addition, there exist certain errors in different processing methods, due to the influence of human factor such as setting parameters during data processing, it is not sure to reflect an exact experiment result actually, so there is an urgent desire for a detection method which is able to acquire an SPR angle more conveniently, quickly and accurately during the process of experiment.